Cure For Distributor Cap Erosion Sought

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First let me acknowledge my weakness in the mysteries of automotive electronics. Secondly I believe I asked this long ago but have forgotten the responses and hope maybe modern technology has advanced since then. My 1917 Maxwell uses an Atwater-Kent coil & distributor system designed to directly replace an existing magneto. This system was retrofitted to many cars of the period and was available in 4, 6 and 8 cylinder versions. Parts are getting hard to find and I'm finding a few caps that appear usable except for having cap material (Bakelite?) burnt away on one side of the inner contacts. Firstly what is causing this on multiple caps and secondly is there any cure to save these burnt caps. I'm 70, been fooling with cars my whole life and have never seen this on any other engines??

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Does this ignition circuit have a capacitor in it somewhere ? If there is one from 1917 it's bad. It would go bad from sitting on the shelf that long. The cap should have a vent hole in the side to vent ionized gas buildup. I have to doubt the burn spot is liable to affect performance. Nice pictures. Your question is well done !

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Does this ignition circuit have a capacitor in it somewhere ? If there is one from 1917 it's bad. It would go bad from sitting on the shelf that long. The cap should have a vent hole in the side to vent ionized gas buildup. I have to doubt the burn spot is liable to affect performance. Nice pictures. Your question is well done !

Thanks for the response and praise. Even though the original capacitor functioned seemingly well enough people smarter than me told me the same as you and I recently replaced it with a modern one. Maybe I waited too long as I see my New Old Stock cap ran only a few hours and now has the same damage shown in my picture of one of my used caps. I just cut the top out of one of my used caps so I can see Exactly where the rotor is as I'm suspecting the ignition is firing after the rotor blade passes the cap contact. That's my theory anyway??

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There is too much resistance in the ignition secondary causing the burning. You can fill the burned out ares like a dentist fills teeth. Be sure you have all new wires, and keep the gap on the plugs tight, and use a hotter plug. The cap will never wear or go bad as long as its not falling apart from age, or warped from bad storage. Also, check your timing, just because the marks line up doesn't mean its correct. I would find TDC on the number one hole, using a physical device and then look at the marks, you may be off five degrees.

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There is too much resistance in the ignition secondary causing the burning. You can fill the burned out ares like a dentist fills teeth. Be sure you have all new wires, and keep the gap on the plugs tight, and use a hotter plug. The cap will never wear or go bad as long as its not falling apart from age, or warped from bad storage. Also, check your timing, just because the marks line up doesn't mean its correct. I would find TDC on the number one hole, using a physical device and then look at the marks, you may be off five degrees.

Thanks for responding. All the ignition parts and wires are new or new old stock. Plugs are used Splitdorfs and that is one thing I could change by getting modern replacements as it would be nearly impossible to get new Splidorfs of any type let alone multiple heat ranges.

Is it possible this problem is strictly the wrong heat range plug?

The coil is an original Atwater-Kent which I know has some kind of resistor built into the ventilated metal cap.

Could that be bad?

Is there any way this coil can be tested as I really would like to use it if at all possible because replacements don't exist that would match original looks.

How would I fill in the damage I have and what should I use? I wondered about grinding an original cap into powder and mixing with some kind of epoxy?

I really appreciate all who have taken the time to help me figure this out as I hate destroying original parts and would like to solve this once and for all and move on to other areas of this restoration.

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Herbrand Coil Tester.......took me thirty year to find one. Go on Youtube and type in the name, and see it working in real time. It LOADS as well as HEATS the coil....the only true working test. Running a DOMV on the bench isn't very helpful, as many shorts only happen after they heat up.

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I am on the road for the next three weeks at shows in the west coast and rust belt. After I return I would be happy to test your coil for you no charge, as long as you enclose a pre made & pre paid return shipping label.

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When I look at your photo it appears the coil fires before the rotor is aligned with the brass electrode in the cap correctly resulting in the spark having to jump a wider gap than normal to the corner of the electrode to fire the spark plug. The spark jumping to that sharp corner could account for excessive erosion of the electrode in that area.

Although the spark timing may be correct, is it possible the opening of the points to fire the coil needs to be synchronized with the rotor in some manner so when the rotor and cap are in proper alignment the spark would jump to the center of the electrode as it should?

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Ed, since I now have that open distributor cap and have the ability to set the rotor to fire at any position what would be the ideal situation considering I have all the levers set to the running position?

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Ronnie, thanks, I was typing my last post as you were answering it. So dead center of the terminal would be ideal?

Howard Dennis

I didn't see where edinmass had made a post about rotor alignment until now. It looks like we are on the same page. I'm not familiar with the distributor you have so Ed would be better qualified to tell you how to adjust the rotor position. I hope aligning the rotor solves your problem.

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Ed, I rushed around this morning and took several photos of my spare system, one good one fair sorry for the out of focus but it does show something helpful. I've been struggling with timing on this car for ages and this latest problem has forced me to rethink it all. It's funny how a problem can haunt you and then revisiting it or talking it over with others can bring solutions you hadn't thought of before. Yesterday I went back and tried to retime the car and after eliminating all the slope in the linkage from 100 plus years in the many joints from the steering wheel quadrant, down the column, across the bellhousing , and forward under the exhaust and intake manifold to the distributor I thought between this action and my now open top cap I could set the rotor perfectly but kept coming up just a hair off dead center of the terminal.

This morning while making these new photos it dawned on me no matter how hard I tried yesterday to position the rotor I had overlooked one last adjustment and that was the ability to remove the set screw below the distributor and lift distributor body and turn rotor 1 tooth to reposition the rotor in the angle drive gears just below the distributor base. In rereading all my literature collected from period repair manuals, Maxwell manuals and even Atwater-Kent installation literature this adjustment is NOT mentioned. My only thought is they all must have thought who would be stupid enough to mess with this factory adjustment. Guess no one thought some restorer 100 years in the future might want to clean and re-grease these gears and might reassemble them slightly off. So my next task is to go back and carefully retime all the obvious adjustments and then see if this newly discovered adjustment can bring the rotor to dead center of the cap terminal.

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Herbrand Coil Tester.......took me thirty year to find one. Go on Youtube and type in the name, and see it working in real time. It LOADS as well as HEATS the coil....the only true working test. Running a DOMV on the bench isn't very helpful, as many shorts only happen after they heat up.

Thanks to Ed for posting this. I was able to find another restoration project by searching for this meter. I believe I've found a Herbrand HT900 Tune Up Center. It includes the HT-660 Coil Tester Ed posted, a Tach Engine RPM Tester HT-864 and a Regulator Tester HT-400. I was able to download a manual on the HT-660 but can't find anything on the other 2 meters. Can anyone supply information on these 2 meters? Even pictures of the test leads for these 2 meters would help me.